Thinning of Greenland Glacier Attributed to Ocean Warming

A new research has attributed the thinning of one of Greenland's largest glaciers to ocean warming preceded by atmospheric changes.

According to the research published in the journal Nature Geoscience, the sudden thinning in 1997 of one of Greenland's largest glaciers, was caused by subsurface ocean warming.

The research team traces these oceanic shifts back to changes in the atmospheric circulation in the North Atlantic region.

The study, whose lead author was David Holland, director of the Center for Atmosphere Ocean Science, part of New York University's Courant Institute of Mathematical Sciences, suggests that ocean temperatures may be more important for glacier flow than previously thought.

The large outlet glacier feeding a deep-ocean fjord on Greenland's west coast, went from slow thickening to rapid thinning beginning in 1997.

Several explanations have been put forward to explain this development.

The scientists in the new study sought to address the matter comprehensively by tracing changes in ocean temperatures and the factors driving these changes.

In doing this, they relied on previous results published by others that used NASA's Airborne Topographic Mapper, which has made airborne surveys along a 120-kilometer stretch in the glacier's ice-drainage basin nearly every year since 1991.

While many other glaciers were thinning around Greenland, these surveys revealed that the particular glacier thickened substantially from 1991 to 1997.

But, after 1997, it began thinning rapidly.

Between 1997 and 2001, Airborne Topographic Mapper surveys showed an approximately 35-meter reduction in surface elevations on the glacier's 15-kilomater floating ice tongue.

This is far higher than thinning rates of grounded ice immediately upstream.

The researchers reported that these changes coincided with jumps in subsurface ocean temperatures.

These temperatures were recorded by the Greenland Institute of Natural Resources from 1991 to 2006 over nearly the entire western Greenland continental shelf.

These data indicate a striking, substantial jump in bottom temperature in all parts in the survey area during the second half of the 1990s.

In particular, they show that a warm water pulse arrived suddenly on the continental shelf on Disko Bay, which is in close proximity of the glacier in question, in 1997.

The arrival coincided precisely with the rapid thinning and subsequent retreat of the glacier.

According to Holland, "The melting of the ice sheets is the wild card of future sea level, and our results hint that modest changes in atmospheric circulation, possibly driven by anthropogenic influences, could also cause future rapid retreat of the Antarctic Ice Sheet, which holds a far greater potential for sea level rise."

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